Aha, I understand that feeling. I don't make skins often, so I usually have this problem regarding my drawings. I think black and pastel should only be in the same piece when one is a foreground, and another is a background. Therefore it doesn't interfere with the design.
Unlike white, black does not go well with every hue and shade, so it can be quite hard to place it in skins or other works. I'm glad my opinion helped.

EDIT: a thing that may help with putting pastel and black together is not making two tone socks. if you make both of them black, it looks much cleaner and well put

oo tysm for telling me! <3